Building a wooden outhouse

[m3coupe]

So after this COVID period and having my family at home constantly, I need an external office to keep the kids and wife away.

I’m wanting to build a 15ft by 10ft wooden outhouse. Plan is concrete base, wooden frame, insulation, cladding outside, plasterboard interior with power.

I was thinking 2x3 to build the frame, 2x6 for the roof straps, fibre wool insulation.

Has anyone completed anything similar? If so, any hints/tips and am I on the right lines with materials?

Also, rough costs for completion? All works completed by myself so no labour costs.

Cheers in advance.